It has been hitherto known in the rubber industry that when a rubber composition containing a filler, such as carbon black, is produced, a rubber wet masterbatch is used to improve the workability of the composition and the dispersibility of the filler. This situation is a situation of mixing the filler and a dispersing solvent beforehand with each other at a predetermined ratio therebetween, dispersing the filler into the dispersing solvent by a mechanical force to yield a filler-containing slurry solution, mixing this slurry solution with a rubber latex solution in a liquid phase, adding a solidifier such as an acid into the mixture to solidify the mixture, and collecting and drying the solidified mixture. In the case of using the rubber wet masterbatch, a rubber composition is obtained which is better in filler dispersibility therein and rubber properties such as workability and reinforceability than in the case of using any dry masterbatch obtained by mixing a filler and a rubber with each other in a solid phase. The use of such a rubber composition as a raw material makes it possible to produce, for example, a pneumatic tire and other rubber products that have a decreased rolling resistance and an excellent fatigue resistance.
In the meantime, it is indispensable for a vulcanized rubber used for tires to be improved in tear-resistance performance and others from the viewpoint of being improved in durability. For this purpose, it is necessary to heighten an interaction between carbon black, which is a reinforcing filler, and the rubber to heighten the dispersibility of carbon black in the rubber.
As a technique for heightening the dispersibility of a reinforcing filler in a rubber composition, Patent Document 1 listed below describes a technique of blending a hydrazide compound and a reinforcing filler into a raw rubber composition.
Patent Document 2 listed below describes a method for producing a master-batch containing a rubber component, a filler and a rubber chemical, in which a first kneader is used to knead the rubber component and the filler and then a second kneader is used to blend the rubber chemical further into the resultant masterbatch.
Patent Document 3 listed below describes a technique of charging 0.1 to 5 parts by mass of a hydrazide compound and 0.2 to 5 parts by mass of zinc flower simultaneously into 100 parts by mass of a rubber component made of at least one from natural rubbers and diene based synthetic rubbers in a rubber mixing and kneading step before the charging of a vulcanizing agent thereinto, and further attaining the mixing and kneading in the state of setting a highest temperature of the system into 130 to 170° C.
Patent Document 4 listed below describes a technique of blending 20 to 150 parts by mass of a filler and 0.05 to 20 parts by mass of a hydrazide compound into 100 parts by mass of at least one rubber selected from the group consisting of natural rubbers and diene based synthetic rubbers.